This is quoted from the dynamic programming card for the min cost climbing stairs problem dp(i)=min(dp(i - 1) + cost[i - 1], dp(i - 2) + cost[i - 2]). I was under the impression that to solve the min cost climing stairs problem the recurrence relation was as follows: dp(i)=min(dp(i - 1) + cost[i], dp(i - 2) + cost[i])? How does one come up with the relation provided in the text?